Sit-on-top, sit-inside kayak and method of producing the same

ABSTRACT

A method of forming a positive-buoyancy watercraft as a seamless, one-piece hollow body with a cockpit including a seat and a recess for a user&#39;s legs is disclosed and claimed. Watercraft and other structures formed by the method are also described and claimed.

FIELD OF THE INVENTION

The invention relates to rotation-molded structures. More specifically, the invention relates to a method of forming a partially-enclosed cockpit in a one-piece molded structure such as a watercraft.

BACKGROUND

Small watercraft such as kayaks, dinghies, paddleboards, surfboards and the like can be manufactured using a rotational molding process similar to that described in U.S. Pat. No. 3,202,745 issued to Ringdal, where a thermoplastic powder or granules are placed in a hollow mold and the mold is heated while being rotated and/or rocked around several axes. The plastic powder or granules coat the inner surface of the mold and fuse together to form the desired object, where the outer surface of the object bears features that are the negative of the inner surface of the mold.

Since articles molded by this process are hollow, they are naturally buoyant. Furthermore, by selecting suitable plastic materials and quantities, strong and durable watercraft may be formed. However, the molding process restricts the possible shape of hulls formed because of the way the product must be removed from the mold. Molds are typically constructed in two pieces (e.g. top and bottom) that are clamped or bolted together during casting. The hull cannot have protrusions or indentations that restrict its removal from the mold. For example, FIGS. 1A-1C show three hull cross-sections. FIG. 1A, section 110 and FIG. 1B, section 120, can be manufactured; but FIG. 1C, section 130 cannot (at least with the mold shown) because the top portion of the hull near 140 prevents the removal of the top half of the mold 150.

A kayak is a small, maneuverable boat fashioned after a craft used by indigenous people in the Arctic regions of North America and Greenland. The pilot sits inside a traditional kayak as shown in FIG. 2A, 210, and the opening to the cockpit is sealed with a waterproof skirt, 220. However, the vessel is not inherently buoyant; if water enters the cockpit, the traditional kayak can founder. A similar craft that is inherently buoyant is shown at FIG. 2B, 230. This boat is known as a sit-on-top kayak (in contrast to the traditional sit-inside kayak) because the pilot sits in a depression 240 formed on the top of the boat. The inside of a sit-on-top kayak is empty, although hatches may be provided so that gear or supplies can be stored inside.

A sit-inside kayak can be formed by rotation-molding a blank and then cutting an opening for the cockpit, and a sit-on-top kayak can be formed by rotation-molding a hull with depressions. However, it has not been possible to form a positively buoyant, sit-inside kayak by rotation molding because the cockpit of such a kayak is an indentation that restricts its removal from the mold.

SUMMARY OF THE INVENTION

A positive-buoyancy watercraft can be formed as a seamless, one-piece hollow body with a cockpit including a seat and a recess for a user's legs by rotation-molding a casting material in a mold that is divided into at least three sections.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.”

FIGS. 1A-1C show cross-sections of three watercraft hulls to illustrate a limitation of rotation molding.

FIGS. 2A and 2B show a traditional kayak and a prior-art sit-on-top kayak.

FIGS. 3A-3C show various views and sections of a watercraft according to an embodiment of the invention.

FIGS. 4A and 4B show molds that can be used to produce a watercraft according to an embodiment of the invention.

FIG. 5 outlines a process by which a sit-on-top, sit-inside kayak may be formed.

FIGS. 6A and 6B show some other structures that can be formed by molds and processes according to embodiments of the invention.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 3A shows a perspective view of a seamless, hollow-bodied kayak 300 with a partially-enclosed cockpit 305 including a seat 365 and a recess for a user's legs. This kayak has the “sit-inside” seating position of a traditional kayak, and also the natural buoyancy of a “sit-on-top” craft. Therefore, it is called a “sit-on-top, sit-inside” kayak. Other features visible in the perspective view include indentations 315, which may be used to hold small items on the deck, a hatch 320 to provide access to the hollow interior, and a splash-guard or “coaming” 310 to direct water that washes across the deck away from cockpit 305.

FIG. 3B shows a cross-section taken at plane 325 in FIG. 3A. The section is roughly perpendicular to a line parallel to the user's legs, and shows two continuous perimeters 330 and 335, the smaller of the two completely contained within the larger. The inside 305 of perimeter 335 is the inside of the cockpit recess, and the outside of perimeter 330 is the outside surface of the hull. The area 340, between 330 and 335, is the hollow interior volume of the kayak. In contrast to this structure, inset 350 shows a similar section taken through a traditional sit-inside kayak. Note that there is only one continuous perimeter; the pilot sits on one side of the surface, and the other side is in contact with the water. Inset 355 shows a similar section through a sit-on-top kayak. Again, there is only one continuous perimeter, and the pilot sits on the same side of the perimeter as contacts the water (from an inside/outside perspective), but at a different place along the circumference.

FIG. 3C shows a second cross-section 360 taken vertically along the centerline of the craft (at A-A as indicated in FIG. 3A). The second cross-section shows how the partially enclosed cockpit 305, seat 365 and leg recess are positioned inside the outer hull. The leg recess may include features such as footwells 370 against which a user can brace his feet. The hollow interior of the craft 340 can be seen in this section also.

Dashed line 375 shows the location of a third cross-section, 380. This section shows how the perimeters described with reference to cross-section 325 may change as the section line approaches the place where the outer hull and inner cockpit join together (near coaming 310). There are still two continuous perimeters 330 and 335, but they are tangent along a portion of their circumferences (see circled areas indicated as 385). The inside of cockpit 305 and hollow hull interior 340 are visible in section 380, also.

The size and shape of the hull may be adapted to the intended user and use. For example, a more-pronounced keel may enhance the vessel's stability and tracking, while a rounder bottom may improve its maneuverability. A flat or square transom 390 may provide a place to mount a rudder for steering or a motor for propulsion. A coaming or splash guard 310 may be formed around the cockpit, and indentations or recesses 315 formed on the deck may provide storage spaces. An opening 320 may be made in the deck to afford access to the hollow interior of the craft, but such an opening should be covered with a watertight hatch cover to prevent water from entering. A round or oval opening can be sealed effectively with a flexible covering that is held in place by elastic tension. A round opening can also be sealed by a threaded hatch cover that screws into a corresponding threaded hatch frame. A rectangular opening (or more generally, an opening that is neither circular nor oval) may require a rigid hatch cover that is held in place by a locking mechanism such as a rotating cam or latch.

Since the kayak is formed as a molded, continuous surface enclosing an interior volume, it has a natural positive buoyancy. Even if the cockpit fills with water, the craft will not sink. In fact, channels or “scuppers” 345 (visible in FIG. 3B) can be formed between the floor or “sole” of the cockpit and the outside of the hull, below the waterline. Such channels can be formed simultaneously with the rest of the craft, as discussed below. If the sole is higher than the waterline (when the craft is floating in its standard orientation), then any water that enters the cockpit will drain out through the scuppers. Thus, a kayak formed according to an embodiment of the invention can be self-bailing.

If desired, a second or even third cockpit can be formed in the continuous surface to accommodate additional passengers, or a single, wide cockpit (with, for example, a plurality of seat depressions arranged across the beam of the craft) can be constructed.

The watercraft described with reference to FIGS. 3A-3C may be formed as a single, seamless, molded, one-piece surface by rotation molding with a multi-section mold as shown in FIG. 4A. A first portion of the mold 410 contains indentations that are the negative of the desired hull bottom. For example, there may be a keel 420 and stepped or scalloped planes 430. A second portion of the mold 440 contains indentations that are the negative of features that will appear on the deck. For example, recesses 315, mentioned above, will correspond to protrusions 450 in the second portion of the mold. The second portion may also contain protrusions or indentations to form a coaming or to mark the locations of hatch openings. The second portion includes at least one opening 460 that corresponds to the partially-endosed cockpit.

Element 470 is a third portion of the mold, which is inserted through opening 460 during the casting process. The outside of this portion of the mold contains features that are the negative of features found inside the partially-enclosed cockpit of the finished watercraft. For example, protrusion 480 will form seat indentation 365, and protrusions 490 will form footwells 370. Mold portion 470 may be hollow, as shown, or solid; the inside area 499 of this portion does not contribute directly to the formation of the watercraft. However, thermal or other effects may make hollow mold portions to perform better.

Note that the top 410 and bottom 440 portions of this mold are shown as material removed from solid, rectangular blocks. This is a simplification for explanatory purposes only; a practical mold would probably contain only enough material outside the inner surface to give the mold adequate stiffness, strength, and thermal properties. It is the inner surfaces of top 410 and bottom 440 molds sections that form the outer surface of the watercraft's hull (in contrast, the outer surface of mold section 470 forms the inner surface of the partially-enclosed cockpit). As is known in the art, smooth or textured (rough, pebbled, ridged, etc.) surfaces can be formed by rotation molding if appropriate negatives of those features are formed on the mold surfaces.

FIG. 5 shows the operations that may occur to mold a watercraft such as that described with reference to FIG. 3. First, a thermoplastic casting material such as a high-density polyethylene (“HDPE”) (available commercially as super linear polyethylene from A. Shulman, Inc.) is distributed in the bottom section of the mold (510). Next, the top section of the mold is secured to the bottom section by clamps, bolts, or the like (520). Then, a third section of the mold (e.g. FIG. 4A, element 470) is inserted through the opening in the top section and secured to the opening with damps or bolts so that the casting material cannot escape from the mold (530). As mentioned earlier, the third section will form the interior surface of the cockpit, and so may contain negative features corresponding to the footwells and seat depression. The third section may also indude protrusions that extend to the inner surface of the bottom section of the mold. The casting material will accumulate around these protrusions to form the scuppers shown in FIG. 3B at 345. Note that the accumulated material may impede the later removal of the third section of the mold, so the protrusions may actually be spacers that are attached to the third section in a way that permits their detachment from the third section while the mold sections are still secured together. For example, spacers may be bolted or screwed to the third section so that the bolt or screw head is accessible from the “inside” 499 of the third section Alternatively, these protrusions may be attached to the first or bottom section of the mold, and simply reach to the third portion when the mold sections are secured together.

Now, the mold is heated and rotated and/or rocked about several axes (540) to melt and distribute the casting material on the inner surfaces of the mold. Once the mold has been heated and rotated for a sufficient time, it is allowed to cool (550) (while continuing to rotate and/or rock, so that the melted casting material does not settle at the bottom of the mold). Then, the first, second and third sections of the mold are separated from each other (560) and the cast watercraft may be removed. If spacers were used to form scuppers, these may need to be disconnected from the mold before the mold pieces are separated. The spacers can be removed after the boat is removed from the mold, leaving channels from the cockpit sole to the bottom of the hull. Finally, plastic flash, mold marks and blemishes may be trimmed from the watercraft (570), and openings for hatches cut, holes for deck rails and accessories drilled, and so forth. (580).

In embodiments with multiple cockpits, the top portion of the mold may have several openings, into each of which a mold part like the third portion described above may be inserted. In some embodiments, the first and second mold sections may form the left and right sides of the watercraft, rather than the top and bottom surfaces. (In other words, the mold line between the first and second sections will be vertical rather than horizontal.) When this type of mold is used, the opening to receive the third section of the mold may be divided between the first and second sections, as shown at FIG. 4B, element 405.

The applications of the present invention have been described largely by reference to a specific example of a one-piece, seamless, hollow, sit-inside kayak. However, those of skill in the art will recognize that similar inherently-buoyant watercraft with partially-enclosed cockpits can also be produced by variations of the method disclosed herein. Furthermore, the favorable strength-to-weight ratio, durability, and relative ease of manufacture of rotational-molded items suggest additional applications for the three (or more) piece molding process described herein. FIGS. 6A and 6B show two other structures that could be formed as described: 6A is a one-piece, hollow auto body 610 with an integral seating area (which corresponds to the cockpit in a watercraft). FIG. 6B is a one-piece, hollow ball 620 with an internal cockpit to hold an adventurous thrill-seeker during a journey down a hill or watercourse. Such similar structures are apprehended according to the following claims. 

1. A structure comprising: a seamless, one-piece, hollow body containing a cockpit formed therein, the cockpit to include a seat and a recess for a user's legs; wherein a section of the body taken perpendicular to a point on a line parallel to the user's legs discloses two continuous perimeters, a smaller of the two perimeters contained within a larger of the two perimeters.
 2. The structure of claim 1, wherein the smaller of the two perimeters is completely contained within the larger of the two perimeters.
 3. The structure of claim 1, wherein the smaller of the two perimeters is tangent to the larger of the two perimeters along a common portion of a circumference of the smaller perimeter and a circumference of the larger perimeter.
 4. The structure of claim 1 wherein the hollow body comprises a watercraft with an elongated shape.
 5. The structure of claim 4, further comprising: a plurality of scuppers to drain water from the cockpit.
 6. The structure of claim 4, further comprising: an opening in a deck of the watercraft, the opening to be covered with a hatch cover.
 7. The structure of claim 4, further comprising at least one of: a recess formed on a top portion of the hollow body; a coaming formed on the top portion of the hollow body; and a keel formed on a bottom portion of the hollow body.
 8. The structure of claim 4 wherein a rear portion of the body forms a flat, substantially vertical transom.
 9. A watercraft comprising: an elongated, molded, continuous surface enclosing an interior volume; and a partially-enclosed cockpit; wherein the surface forms two lateral sides of the cockpit, a sole of the cockpit, and a deck covering a portion of the cockpit.
 10. The watercraft of claim 9, wherein the surface is formed as a single unit.
 11. The watercraft of claim 9, further comprising: at least one channel to connect the sole of the partially enclosed cockpit with an outer surface of the watercraft, wherein one end of the at least one channel is below a waterline of the watercraft in the watercraft's standard orientation.
 12. The watercraft of claim 9, further comprising: a covered hatch to provide access to the interior volume through the continuous surface.
 13. The watercraft of claim 12, wherein the covered hatch is oval in shape, the watercraft further comprising: a watertight hatch cover constructed of an elastic material, the hatch cover to seal to the hatch by elastic tension.
 14. The watercraft of claim 12, wherein the covered hatch is rectangular in shape, the watercraft further comprising: a watertight hatch cover constructed of a rigid material, the hatch cover to seal to the hatch by a locking means.
 15. The watercraft of claim 12, wherein the covered hatch is circular in shape, the watercraft further comprising: a watertight hatch cover constructed of a rigid material, the hatch cover to seal to the hatch by a screw means.
 16. The watercraft of claim 9, further comprising: a second partially-enclosed cockpit, wherein the continuous surface forms two lateral sides of the second cockpit, a floor of the second cockpit, and a deck covering a portion of the second cockpit.
 17. A method of forming a structure comprising: securing a first section of a mold to a second section of the mold; placing a casting material into the mold; inserting a third section of the mold through an opening in the mold; securing the third portion of the mold so that the casting material cannot escape from the mold; and simultaneously rotating the mold and heating the mold to melt and distribute the casting material.
 18. The method of claim 17, further comprising: placing at least one spacer between the third section of the mold and one of the first section of the mold and the second section of the mold.
 19. The method of claim 17, further comprising: inserting a fourth section of the mold through a second opening in the mold; and securing the fourth section of the mold so that the casting material cannot escape from the mold.
 20. A mold comprising: a first section to form a first portion of a surface of a watercraft; a second section to form a second portion of a surface of the watercraft; and a third section to form a third portion of a surface of the watercraft, wherein the first and second sections are to be secured together; when the first and second sections are secured together, an opening to an interior of the mold remains; and the third section is to be inserted into the opening and secured to the opening.
 21. The mold of claim 20, further comprising: a protrusion in the first section to form a recess in the first portion of the surface of the watercraft.
 22. The mold of claim 20, further comprising: a protrusion in the third section to form a seat depression in the third portion of the surface of the watercraft.
 23. The mold of claim 20, further comprising: a spacer to be inserted between the third section and one of the first section and the second section, wherein a fastener to connect the spacer to the third section is accessible when the sections of the mold are secured together. 